1. Field of the Invention
The present invention is generally directed to gage sensing systems and methods for inspecting railroad tracks. More specifically, the present invention is directed to an electromagnetic gage sensing system and method.
2. Description of the Related Art
Gage sensors and sensing systems currently used by various U.S. railroads to measure and inspect gage distance between rails of a railroad track are generally based on optical, mechanical contact, or electromagnetic measurement technologies.
The optical gage sensing systems and methods that use optical technologies provide high level of accuracy but have inherent weather and reliability limitations. Such optical gage sensing systems are readily effected by rain, snow, dirt, and other environmental conditions. In addition, such optical gage sensing systems require periodic cleaning of lenses or protective windows to remove dirt, grease, oil, and other substances typically present in the railroad environment. Such optical gage sensing systems are also known to become saturated and provide inaccurate readings when sunlight reflected by the shiny rail surface reflects directly into the sensing system.
The performance and accuracy of mechanical contact gage sensing systems and methods are not as sensitive to weather conditions as optical gage measurement sensing systems. However, such contact gage sensing systems are not sufficiently reliable or accurate. In particular, contact gage sensing systems often become damaged by switches and other objects near the railroad track, thereby decreasing the accuracy and reliability of the resultant measurement. Contact gage sensing systems also require frequent maintenance due to the normal wear and tear of contact wheels or other contacting components that are typically used in such systems.
An electromagnetic gage sensing system and method of measurement has been developed that utilize a single proximity sensor to determine the distance to the gage surface of the rail. An electro-mechanical tracking system is used in conjunction therewith to continuously adjust the proximity sensor's position to maintain a fixed distance between the proximity sensor and the rail of the railroad track. The proximity sensor is located below the top of the rail and near the rail gage surface. However, the electromagnetic gage sensor, as described is not reliable because the sensor is easily damaged by switches, grade crossings, and other obstructions that may be present along the railroad track. Correspondingly, the electromechanical tracking system requires periodic servicing and maintenance which increases costs associated with operating such a system.
Japanese Patent 55-52901 issued to Shirota et al. discloses a non-contact measurement of gage between the rails of a railroad track by detecting the change in impedance due to magnetic induction, such as eddy current. A pair of detectors are positioned directly over the contact surface of the rails to allow determination of the rail position. In addition, another pair of detectors are angled toward the inner surface of the rails to allow determination of the gage distance between the rails of the railroad track. The pairs of detectors are mounted on a mounting base so that they are fixed at a predetermined position. The gage distance between the rails of the railroad track is calculated in accordance with an equation disclosed in the reference.
The main disadvantage of the solution proposed in Japanese Patent 55-52901 is that high level of accuracy of gage measurements cannot be achieved due to the significant lateral motion of the rail of up to 60–70 mm, relative to the sensor mounting location. This lateral motion is caused by continuous changes in position of the rail vehicle bogie where the detectors are mounted, relative to the rails of the railroad track. The width of the rail head of the railroad track is typically 50 mm. To obtain accurate data, the height above the rail should be measured at the center of the rail head while the gage should be measured slightly below the top of the rail. However, due to the significant motion of the detectors relative to the rail, the detectors point to wrong locations on the rails of the railroad track so that the obtained measurements are inaccurate.
The above noted disadvantage and limitation of the system disclosed in Japanese Patent 55-52901 is compounded by the fact that the proposed solution of this reference is also sensitive to rail metal composition. In particular, the detectors used in the disclosed system operate based on the magnitude of the magnetic induction measurements. However, magnitude of the magnetic induction measurements vary depending on the material of the rail, i.e. the metal composition of the rail. When an inspection car moves along the railroad track, the material properties of the rails of the railroad track will change, based on various parameters such as oldrail versus new rail, different types of rail, rust and so on. All of these variations cause changes in the magnitude of the output thereby limiting the accuracy of the measurements obtained utilizing such a system.
Therefore, there still exists an unfulfilled need for a system and method for a non-contact electromagnetic gage measuring system. There also exists a need for such a system and method that provides reliable and accurate gage and/or height measurements for rails of the railroad track. In addition, there further exists an unfulfilled need for such an electromagnetic gage sensing system and method that is resistant to environmental conditions and rail metal composition.